1. Industrial Field of Utilization
The present invention provides a saponified ethylene-vinyl acetate copolymer composition markedly improved in long run property in melt-molding and in quality.
2. Prior Art
Saponified ethylene-vinyl acetate copolymers are excellent in various properties such as oxygen barrier property, mechanical strength, etc., and therefore have found application in various uses such as film, sheet, container material, textile fiber and so on.
However, since such saponified copolymers are highly hygroscopic, shaped articles based on these materials are disadvantageous in that they undergo marked change in physical properties such as flexibility according to changes in the humidity and temperature of the ambient atmosphere and, in particular, their oxygen barrier property is so highly dependent on humidity that they do not effectively seal off oxygen in a high-humidity environment.
Furthermore, because of poor stretchability and flexibility, shaped articles based on this type of copolymer readily undergo uneven stretching in the course of deep-drawing or other molding procedures involving stretching and/or give pinholes in use after molding, imposing limitations on their use as packaging materials. Therefore a polyolefin resin is often admixed with said saponified copolymers.
However, such resin mixtures as mentioned above are inferior in the so-called long run property. When they are used to produce films, sheets and the like shaped articles by melt-molding, for instance, said mixture compositions undergo gelation during molding and/or give, during molding, thermally discolored or carbonized resins (the so-called scorches), which adhere to the extruder interior. Accordingly the melt molding cannot be done continuously for a prolonged period of time. To cope with this problem, the combined use of a hydrotalcite solid solution has been proposed as a measure therefor.